A woman was sexually assaulted on board a train to Manchester.
Detectives from British Transport Police have issued a CCTV image of a man they want to speak with.
Anyone with information is being urged to come forward. The force said a man sat down on a chair next to the woman then sexually assaulted her.
She is said to have 'challenged' him, before he stood up and moved to another seat.
The attack happened at around 8.30pm on February 18, but details of the incident have only just been released.
No further details have been revealed.
No age for the woman has been confirmed either.
It happened on board a service from London Euston to Manchester Piccadilly and the CCTV is the best quality currently available.
British Transport Police have issued a public appeal which is also running on social media.
A BTP spokesman said: "Do you recognise this man?
"Officers would like to identify him in connection with a sexual assault on board a train from London Euston to Manchester Piccadilly.
"On 18 February at approximately 8.30pm, a man sat next to a woman on board the train service before sexually assaulting her.
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"The victim then challenged him, and he got up and sat in a different seat.
"Officers believe the man in the CCTV image may have information which could help their investigation."
Contact BTP by texting 61016 or calling 0800 40 50 40, quoting reference 1900013743.
Alternatively, anyone with information can call Crimestoppers, anonymously, on 0800 555 111.
